Continually rotating electrical motor have a great variety of uses, many of them occurring within the data processing industry. One of the most significant of these uses is in magnetic media disk drives, some of them being used for flexible of "floppy" disk drives and some being utilized in hard, fixed or "Winchester" disk drives. The type of performance required for these utilizations is high speed rotation with extremely steady performance. The motors should be capable of starting readily and achieving an equilibrium running state in a short time.
Once all of the above characteristics have been achieved, improvements in the motors can be accomplished by cutting the cost of manufacture, simplifying the necessary associated circuitry and reducing the size of the motors, among other possibilities. Improvements have been made in various aspects, including improving the start-up capabilities of the motor. A prior art motor which shows enhanced start-up capabilities and is otherwise typical of the construction of brushless DC motors is found in the Inventor's prior patent entitled "Brushless DC Motor Assembly With Improved Stator Pole", U.S. Pat. No. 4,499,407.
Other examples of brushless DC motors incorporating conventional structures and associated circuitry may be found in U.S. Pat. No. 4,430,603, issued to Muller and U.S. Pat. No. 4,376,261 issued to von der Heide et al.
One of the most common forms of brushless DC motors in the prior art is the three phase bipolar excitation type of motor. Another is the two phase unipolar excitation type.
The three phase bipolar version is popular since it provides high performance characteristics. However, in addition to relatively complex commutation logic and circuitry, this type of motor requires three separate stator windings and six switching devices to achieve proper motor control.
The two phase unipolar excitation type motor, an example of which may be found in U.S. Pat. No. 4,429,263, issued to Muller, has long been thought to be the simplest form of operable motor. This type of motor requires two separate stator windings and two switching devices, plus a position sensor and commutation logic and circuitry.
With each effective type of brushless DC motor the goal is to achieve an array wherein, regardless of the position of the rotor with respect to the stator during rotation, a positive torque is generated. This has been accomplished in the above motors by the multiple windings and switching devices, with the appropriate ones being activated depending on rotor position.
All of the prior art brushless DC motors within the inventor's knowledge have utilized at least two excitation pulses per pair of poles per rotation or else have required some variety of mechanical initiation of rotation. An example of a motor using a single excitation pulse but an external mechanical rotation initiator is found in the standard high school laboratory project wherein a bar magnet is rotatably mounted within an armature coil having commutating brushes to switch the polarity of the current in the armature coil. As those skilled in the art will recall, this sort of motor will spin happily once it has started but the ordinary method of initiating rotation is to manually spin the magnet within the armature upon initiation. This is required because there are dead spots, or zero torque zones, wherein the application of current will not cause the motor to initiate rotation. Obviously, the requirement of a manual rotational initiation step is not desirable in an enclosed motor within an operational device.
No prior art DC motor to the inventor's knowledge has successfully utilized brushless multipole technology with a single excitation phase pulse or a single switching device. All successful applications to date have used more complex electrical structures or have required additional external rotational impetus.